Twenty percent of liquid tumors of the ovary are persistent functional cysts. Laboratory tests of the cystic fluid should make it possible to distinguish between functional cysts and organic cysts. In 170 patients derived from a multicenter study and presenting with a liquid tumor of the ovary (including 9% of cancers), samples of the cystic fluid and serum were taken from the patient and the ACE, CA 125, CA 19-9 markers, estradiol and Progesterone were assayed. The results of these assays were subjected to computerized analysis and compared with the pathological findings. The assays were able to discriminate between organic cysts and functional cyst with 93% of sensitivity and 95% specificity. The insufficient reliability of this evaluation justified a second study (in progress) which is limited to the study of pure fluid tumors with thin walls, no partitions, no vegetations and measuring less than 8 cm in diameter in which the incidence of cancers is very low. This study should fine tune the initial findings and result in a sensitivity approaching 100 percent. If this hypothesis is confirmed, it should be possible to include ultrasound-guided puncture carried out under closely defined conditions in the therapeutic decision trees for liquid cysts of the ovary.